Tuesday, July 17, 2007

Strap a Sterling Engine to a refractor dish and you get:

"The Stirling engine makes solar power so much more efficiently than photovoltaic solar cells can," said Robert Liden, chief administrative officer at Stirling Energy Systems Inc. (Phoenix). "That's because the Stirling solar dish directly converts solar heat into mechanical energy, which turns an ac electrical generator." The bottom line, he said, "is that large farms of Stirling solar dishes — say, 20,000-dish farms — could deliver cheap solar electricity that rivals what we pay for electricity today."

Eventually, according to DOE estimates, an 11-square-mile farm of Stirling solar dishes could generate as much electricity as the Hoover Dam, and a 100 x 100-mile farm could supply all the daytime needs for electricity in the United States. By storing the energy in hydrogen fuel cells during the day, Stirling solar-dish farms could supply U.S. electrical-energy needs at night too, as well as enough juice for future fuel-cell-powered automobiles, the DOE believes.

Power today costs from about 3 cents to 12 cents per kilowatt-hour, depending upon the customer's location and the time of day. The average is 6.6 cents/kW-hr for the industrial sector in 2004, according to DOE. In contrast, the Stirling solar-powered substations operate only during peak hours (daytime) but at potentially the same or less than the peak rates paid today — or "about 6.5 cents per kilowatt-hour during peak periods," said Liden of Stirling Energy Systems.

A Sound Way to Turn Heat into Electricity

University of Utah physicists have developed small devices that turn heat into sound and then into electricity. The technology holds promise for changing waste heat into electricity, harnessing solar energy and cooling computers and radars.

"We are converting waste heat to electricity in an efficient, simple way by using sound," says Orest Symko, a University of Utah physics professor who leads the effort. “It is a new source of renewable energy from waste heat."

In the above photo, Symko demonstrates how heat can be converted into sound by using a blowtorch to heat a metallic screen inside a plastic tube, which then produces a loud tone, similar to when air is blown into a flute. Symko and his students are developing much smaller devices that not only convert heat to sound, but then use the sound to generate electricity.

Symko plans to test the devices within a year to produce electricity from waste heat at a military radar facility and at the university's hot-water-generating plant.

Symko expects the devices could be used within two years as an alternative to photovoltaic cells for converting sunlight into electricity. The heat engines also could be used to cool laptop and other computers that generate more heat as their electronics grow more complex. And Symko foresees using the devices to generate electricity from heat that now is released from nuclear power plant cooling towers.